Cover thread pulling and take-up device for multineedle sewing machines

ABSTRACT

A multineedle sewing machine having a cover thread pulling device which is linked to a cover stitch device comprising an upper looper. The cover thread pulling device is fixed near the upper looper and moves integrally therewith to exercise a pull of the cover thread without being influenced by the stretching of the thread due to the latter&#39;&#39;s elasticity which is now negligible due to a shortening of the length of the thread exposed to the action of the thread pulling device.

United States Patent [191 Mariorio COVER THREAD PULLING AND TAKE-UP DEVICE FOR MULTINEEDLE SEWING MACHINES {75] Inventor: Nerino Marforio, Milan, Italy [73] Assignee: S.p.A. Virginio Rimoldi & C., Milan,

Italy 22 Filed: Oct. 10, 1973 21 Appl. No.: 405,033

:30] Foreign Application Priority Data 0a. 20, 1972 Italy 30712 72 :52] US. Cl. 112/243 '51] Int. Cl D05b 49/00 58] Field of Search 112/241, 242, 243, 163, 1 12/165 56] References Cited UNITED STATES PATENTS .,l33,608 3/1915 Berger 112/242 X 51 May 13,1975

1,557,135 10/1925 Berger 112/242 1,711,483 5/1929 Allen et a1.

2,174,205 9/1939 Ebert 2,350,965 6/1944 Muecke 2,996,023 8/1961 Pollmeier 112/241 X Primary ExaminerGeorge H. Krizmanich [57] ABSTRACT A multineedle sewing machine having a cover thread pulling device which is linked to a cover stitch device comprising an upper looper. The cover thread pulling device is fixed near the upper looper and moves integrally therewith to exercise a pull of the cover thread without being influenced by the stretching of the thread due to the latters elasticity which is now negligible due to a shortening of the length of the thread exposed to the action of the thread pulling device.

4 Claims, 5 Drawing Figures PATENTEI] MAY 1 31975 SHEET 10F 4 PATENIED W 1 3&975

SHEET 2 OF 4 FATENTEQ KAY I 36975 SHEET 4 BF 4 COVER THREAD PULLING AND TAKE-UP DEVICE FOR MULTINEEDLE SEWING MACHINES The present invention relates to a thread pulling device for a multineedle sewing machine cover thread, the said device being linked to a cover stitch device complete with upper looper, and fitted with a movable thread take-up element functionally connected to the said cover stitch device, the whole so designed as to act directly on the cover thread.

Thread pulling devices of this kind are already well known in the art, but the thread take-up element acting directly on the cover thread so as to allow it to run freely to the workpiece during the stitching operation and to pick it up at the end of thereof, has drawbacks exercising a negative influence on the sewing operation.

These drawbacks are mainly caused by the said thread pulling device being normally fixed to the sewing machines at a point away from the relative cover stitch device.

For this reason, there is a considerable length of thread stretched out between the said devices, this length being subjected to continuous alternating stress oscillations, being lengthened and again shortened for each stitch to be made.

The thread used for cover stitching is very elastic and the excessive length of thread between the two devices is impairing its soundness.

The great distance separating the two devices exercises a till further negative effect in that the thread, to follow the profile of the machine, has to pass through a great number of thread guides with the therefrom excessive wear caused by the metal parts of these guides. A still further negative effect is that the kinematic chain for their operation requires a great number of mechanical parts which, obviously, will have a negative influence on the timing values interlinking the two devices, and which are caused by the small mechanical errors inevitably appearing in a mechanical transmission chain.

Finally, the action of the thread pulling devices too results to be somewhat imperfect and not very efficient as regards the perfect and uniform formation of the cover stitches, resulting very often in the wrinkling of the workpiece and stressing at the point of sewing. In fact, the thread pulling device of the known kind is subjected to an oscillating motion which, for each stitch, rhythmatically first tightens and then releases the thread, lengthening thus each time the real path to be covered, this to pick up part of the excess of thread inserted into the stitches to be formed, and to recall at the same time from the spool the length of thread which, at the end of the cycle, is absorbed by the stitch.

Obviously, the thread, to be able to respond in the best way to the action of the pulling and pick-up device, must first be drawn out so as to take up all of its elasticity, and then moved. Thus the threads natural internal tension is increased until reaching its maximum drawn-out length when the said device will impress on it the required forward motion. For this reason the thread must be sufficiently prestretched to maintain it at the required length for being able to respond as soon as possible to the action of the pulling device. It is obvious that the pretensioning of the thread required to keep the latter stretched out to the limit of its resistence and capable of eliminate its natural elasticity, must have a very high value.

It follows therefrom that the thread will be negatively influenced because of the straining action generated by the tension discs the thread is passing through.

It is the object of the present invention to eliminate the above-mentioned drawbacks so as to obtain seams in which all the threads are well interlinked and laid and in which the elasticity of the threads does not leave any traces.

To reach this object, the technical problem to be resolved mainly consists in reducing the distance between the thread pulling device and the cover stitch device, as well as in changing the laws of motion of the thread pulling device so as to ensure a more suitable and efficient action of the cover thread when forming the single points.

The said problem is resolved by providing a thread pulling device of the above type, in which a movable thread pulling element is fixed to the drive shaft of the cover stitch device, the latter carrying the upper looper, and in which the said thread pulling element is fixed to and integrally moving with the said upper looper. This new arrangement results in a sensible shortening of the length of thread periodically exposed to the action of the thread pulling device, which, therefore operates without being influenced by the stretching of the thread due to the latters elasticity which is now negligible.

This results in the formation of aesthetically perfect and uniform seams with the cover stitch thread well tensioned between the corresponding sewing stitches.

It is obvious that also the structure of the thread pulling device acting on the cover thread, has an influence of the quality of the seams. In fact, it is not sufficient that the thread pulling device periodically increases the length of the thread to form a loop permitting at the same time the lengthening of that part of the thread available for the cover stitch device for forming good stitches, but it is also necessary that the thread be handled according to a particular law ensuring that the taking up of the excess thread tightens the stitches without causing wrinkling or an excessive tightening of the finished seam.

It is hence necessary to exert a short initial jerk causing the thread to be stretched, keeping it stretched until the wire from the stitches has been fully taken up and exert then a rather violent final pull to definitely tighten the stitch and recover the length of thread successively used up by the stitches from the spool. For this reason the above-mentioned technical problem is also resolved by providing the thread-pulling element with an attachment for connecting it to the cover stitch device drive shaft and a centre part connected at one side to the said attachment shaped as offset at the other side with the free end opportunely bent back to prevent the thread from sliding off; the said centre section being displaced with respect to the line joining the said attachement to the free end; the displacement being such as to determine the said offset provided as a temporary obstacle against the cover thread prematurely leaving the said centre section which exercises a constant and uniform pull on the said thread; the said free end being designed so as to exercise a final pull on the cover thread to tighten the stitch being formed and recall at the same time from the spool a length of thread which is sufficient to form a new stitch. It is evident that this new characteristic has the advantage of permitting the formation of a perfect and safe tightening of the stitch, which cannot be obtained without the final pull.

Other characteristics and further advantages will be evidenced by the following description and the accompanying drawings given by way of example without limiting the range of the present invention, and in which:

FIG. 1 is a sectional view of the object of the present invention applied to a sewing machine of the abovementioned type;

FIG. 2 is a section along linr II-II of FIG. 1;

FIG. 3 is an enlarged plan of the thread-pulling device here referred to;

FIGS. 4 and 5 schematically show two different phases of stitching complete with cover stitch.

Referring now to FIG. 1, the thread pulling device 10, object of the present invention, is fixed to a multineedle sewing machine and linked to a cover stitch device 11.

The said sewing machine comprises a frame provided with an arm 12 over a base (not shown) fitted with the table 13 which receives the workpiece during the sewing operation.

A drive shaft 14 is fixed in the manner of a rock shaft inside of the arm 12 and is fitted with a lever arm 15 hinged to a link 16 for transmitting the rocking movements of the said drive shaft to the cover stitch device 11.

The said device consists of an oscillatably driven drive shaft 17 provided at the top with an arm 18 connected in turn to the link 16. The other end of the drive shaft 17 projecting from the bottom of the frame, carries a clamp 19 of the thread pulling device 10 (FIG. 2) and a support 20 for the upper looper 21 of the cover stitch device.

The said upper looper is positioned near the table 13 and is provided for gripping the thread 22 so as to tenter it as required among the threads (not shown) carried by the needles 23 of the sewing machine. The thread pulling device 10 comprises in addition to the said clamp 19 also an opportunely shaped rod which defines a thread-pulling element 24 adjustably fixed to the said clamp 19 and which moves integrally with the upper looper 21. A plate 25 is fixed with screws 26 to lower part of arm 12 of the machine near the cover stitch device and also very near to the support 20 of the upper looper 21. The plate 25 (see also FIG. 3) is provided with two parallel lugs 27 each of which neing provided with a hole 28 through which passes the cover thread 22 leading to the upper looper 21.

The thread guide lugs 27 are linked together by a crossbar 29 which acts as spacer and connects them at the same time to plate 25. In the space formed by the two lugs operates a thread-pulling element 24 cyclically oscillating in and out of the said space. The movement of the said thread-pulling element 24 between the said thread guide lugs 27 is provided for generating a loop in the thread and lengthen it for having sufficient thread available at the stitches for ensuring the perfect tightening of the latter and, at the same time, allowing sufficient thread to be taking up at the spool for replacing that used up for making the stitch. The plate 25 is also fitted with a shaped tailpiece 30 carrying a disk tensioning element 31 for passing the cover thread 22 and a pair of thread guides 32 positioned between the said tensioning element and a standard thread spool (not shown).

Finally the sewing machine comprises the known presser device of which only the presser bar 33 is shown; a needle clamp 34 is fixed to the lower part of the needle bar 35 which slides vertically in the said arm 12.

As well known, the upper looper 12 is provided to grip by means of the gripping point 36 the cover thread which normally runs at the right of the needles 23 and shift it to the left thereof and link it to the thread carried by each of them.

Along the path between the thread-pulling device 10 and the upper looper 21, the thread is guided by the thread guides 37,38,39. The first one is at the top to lead the thread coming from the thread pulling device to the second one at the bottom near the gripping zone. The third one is fixed to the needle clamp 34 and follows the movements of the latter during its vertical displacement during the making of a stitch.

With reference to FIG. 3, the thread-pulling device 24 is so shaped as to possess a centre section 40 linked at one side to an attachment 41 designed to be inserted into the clamp 19, and having at the other side a free end 42 opportunely curved to prevent temporarly the thread to slide off. The centre section 40 is rather displaced relative to the position of the link A joining the attachment 41 to the curved up end 42 to ensure that the said centre section 40 contact the thread 22 stretched out between the two holes 28 before the said end. The above displacement, defines a bend 43 in the thread pulling element 24, which, because of the motion the latter carries out together with the clamp 19 around the axis of the drive shaft 17 of the cover stitch device 11, serves as temporary obstacle against the rapid sliding off of the thread 22 from the centre section 40 toward the curved up end 42.

With particular reference to FIGS. 3, 4 and 5, the object of the present invention has been linked by way of example without being limited thereto, to a multineedle interlock, double-locked chain stitch sewing machine which, as known, has only one main looper.

The cover stitch and the sewing stitch are made simultaneously, because the thread 22 is locked to the needle threads 45 opportunely held back by the main crochet 46 operating beneath the table 13 of the machine.

At the beginning of the cycle, the main looper 46 moves forward to grip in turn all the needle threads 45 carried by the needles 23 all lowered; the upper looper 21 moves from the right to the left relative to the said needles 23 to grip the cover thread 22 having been fed forward by the lower thread guide 38, whilst the intermediate thread guide 39 is near the lower one, perfectly in line with the latter and the upper one 37. The thread-pulling element 24, following the movement of the upper looper 21, approaches the holes 28 of the thread guide lugs 27 to reduce speedily its own action on the thread 22. The needles in this phase moving upwards, also the intermediate thread guide 39 moves away from the lower one 38 to approach the upper one 37 until being side by side with the latter and lengthening thus the path of the thread 22.

For this reason the thread 22 will always be well stretched because during the downstroke of the needles the thread is exposed to the action of the pulling element 24 and during the upstroke of the needles is simultaneously stretched by the intermediate guide 39 and the moving workpiece.

This ensures the safe take-up of the thread by the upper looper. At the end of this phase the main looper 46 has fully moved forward and, with the needle threads held back on its blade 47, the upper looper 21 is shifted to the left of the needles 23 with the cover thread so arranged as to be easily retained by the needles which have reached in the meantime the upper stop, while the thread-pulling element has reached its innermost position between the guide lugs 27.

At this point the above-mentioned movements are reversed to start the return stroke and finish the cycle.

The main looper 46 moves back to permit the forming of of a new series of stitches; the needles 23 move downwards carrying with them also the length 22a of the cover thread 22 in the meantime left free by the upper looper 21. The thread-pulling device recovers thread by the action of the thread-pulling element 24, the centre section 40 of which is now almost in contact with the cover thread stretched out between the holes 28, while the curved end 42 is held back near the crossbar 29 in the space formed by the thread guide lugs 27. As soon as the upper looper 21 begins its return stroke, the centre portion 40 exercises a thrust onto the said thread and, being nearer the drive shaft 17, moves together with the latter but slower than the curved end 42, and exercising a uniform and constant thrust thereon. The thread is forced to follow this movement for a certain time, at the end of which it will overcome the obstacle created by the bend 43 and slide onto the bend end 42 which, being now farther away from the said shaft 17, moves in a faster manner.

This difference in speed causes a sharp pull on the cover thread 22, resulting, as already outlined, in the perfect tightening of the formed stitch and the feed in, from the spool over the tensioning disc 31, of a certain length of thread sufficient to compensate that taken up by the stitch.

Given the fact that the length of thread stretched out between the tensioning element 31 and the thread guide 37 is substantially rather short when compared to the elasticity of the thread and hence rather insensible to lengthening, the forces used to tensioning the cover thread are relatively small and do not compromise the integrity of the thread, ensuring at the same time a perfect stitch.

Finally, the thread pulling element 24 being adjustably fixed to the clamp 19, its travel for each cycle can be varied; positioning it nearer or farther away from the drive shaft 17, it is possible to obtain a smaller or greater feed in of thread and a smaller or greater tightening pull at the end.

What is claimed is:

1. A cover stitch device for sewing machines of the multi-needle type comprising:

a. an oscillatable drive shaft having an upper looper carried on one end of and moveable with said drive shaft;

b. a thread pulling element operatively connected to said drive shaft and movable with said upper looper in a first direction to draw and hold under tension a predetermined amount of cover thread from its source and in a second direction to release the cover thread to the upper looper for its presentation to the stitches being formed by the needles of the sewing machine.

2. The device according to claim 1 wherein said thread pulling element defines a rod member having one end adjustably clamped to said drive shaft, an offset center section for exercising a constant and uniform pull on the cover thread while moving in the first direction with said drive shaft and a curved free end for exerting a sharp final pull on the cover thread for tightening the previously formed stitch and withdrawing a sufficient amount of cover thread for the subsequent stitch.

3. The device according to claim 2 wherein said cover stitch device includes a pair of spaced parallel lugs (27) having aligned holes (28) through which the cover thread extends and between which said off-set center section of said thread pulling element is movable to draw and tension the thread as it moves in its first direction of travel.

4. The device according to claim 2 wherein said curved free end of said thread pulling element is located a greater distance from said drive shaft than said off-set center section so as to move at a faster rate than the latter to increase the linear speed of the thread during the final pull of said thread pulling element in its first direction of travel. 

1. A cover stitch device for sewing machines of the multi-needle type comprising: a. an oscillatable drive shaft having an upper looper carried on one end of and moveable with said drive shaft; b. a thread pulling element operatively connected to said drive shaft and movable with said upper looper in a first direction to draw and hold under tension a predetermined amount of cover thread from its source and in a second direction to release the cover thread to the upper looper for its presentation to the stitches being formed by the needles of the sewing machine.
 2. The device according to claim 1 wherein said thread pulling element defines a rod member having one end adjustably clamped to said drive shaft, an off-set center section for exercising a constant and uniform pull on the cover thread while moving in the first direction with said drive shaft and a curved free end for exerting a sharp final pull on the cover thread for tightening the previously formed stitch and withdrawing a sufficient amount of cover thread for the subsequent stitch.
 3. The device according to claim 2 wherein said cover stitch device includes a pair of spaced parallel lugs (27) having aligned holes (28) through which the cover thread extends and between which said off-set center section of said thread pulling element is movable to draw and tension the thread as it moves in its first direction of travel.
 4. The device according to claim 2 wherein said curved free end of said thread pulling element is located a greater distance from said drive shaft than said off-set center section so as to move at a faster rate than the latter to increase the linear speed of the thread during the final pull of said thread pulling element in its first direction of travel. 